你如何正确地对一个自由浮动的 space 物体施加重力，并在向相反方向推进时产生某种摩擦力

Question

我正在尝试编写基本上类似于小行星的运动程序，一旦按下向上按钮，您就会加速到某个速度，然后因为在 space 中您不会停下来，只能通过推入来减速相反的方向。最重要的是，我希望重力将您拉向屏幕底部。我已经完成了大部分工作，但我遇到的问题是：

当我转身反方向冲刺时，它并没有先向后减速再开始向前运动，而是全速向相反方向射出

关于如何处理此问题并使移动总体上更流畅的任何建议？

import pygame as pg
import os
vec = pg.math.Vector2

TITLE = "GRAVITAR"
WIDTH = 800
HEIGHT = 600
FPS = 60
GREY = (211, 211, 211)

# Player properties
ROCKET_SHIP = 'Images/Rocket_Ship.png' # <a href='https://pngtree.com/so/spaceship-clipart'>spaceship 
                                       # clipart png from pngtree.com</a>
PLAYER_ACC = 0.5
PLAYER_FRICTION = -0.00
PLAYER_GRAV = 0.1
PLAYER_ROT_SPEED = 200
PLAYER_SPEED = 5

class Player(pg.sprite.Sprite):
    def __init__(self, game, x, y):
        pg.sprite.Sprite.__init__(self)
        self.game = game
        self.image = game.rocket_ship
        self.rect = self.image.get_rect()
        self.rect.center = (x, y)
        self.vel = vec(0, 0)
        self.pos = vec(x, y)
        self.rot = 0

    def get_keys(self):
        self.rot_speed = 0
        self.acc = vec(0, PLAYER_GRAV)
        keys = pg.key.get_pressed()
        if keys[pg.K_LEFT]:
            self.rot_speed = PLAYER_ROT_SPEED
        if keys[pg.K_RIGHT]:
            self.rot_speed = -PLAYER_ROT_SPEED
        if keys[pg.K_UP]:
            self.vel = vec(PLAYER_SPEED, 0).rotate(-self.rot)
        if keys[pg.K_SPACE]:
            self.shoot()
        self.acc += self.vel * PLAYER_FRICTION
        self.vel += self.acc
        if self.vel[1] >= 2:
            self.vel[1] = 2
        self.pos += self.vel + 0.5 * self.acc

    def shoot(self):
        pass

    def update(self):
        self.get_keys()
        self.rot = (self.rot + self.rot_speed * self.game.dt) % 360
        self.image = pg.transform.rotate(self.game.rocket_ship, self.rot - 90)
        self.rect = self.image.get_rect()
        self.rect.center = self.pos
        self.pos += self.vel * self.game.dt
        if self.pos.x > WIDTH:
            self.pos.x = 0
        if self.pos.x < 0:
            self.pos.x = WIDTH
        if self.pos.y > HEIGHT:
            self.pos.y = 0
        if self.pos.y < 0:
            self.pos.y = HEIGHT

class Game:
    def __init__(self):
        # Initialize pygame and create window
        pg.init()
        pg.mixer.init()
        pg.key.set_repeat(10, 50)
        os.environ['SDL_VIDEO_WINDOW_POS'] = '568, 101'
        self.screen = pg.display.set_mode((WIDTH, HEIGHT))
        pg.display.set_caption(TITLE)
        self.clock = pg.time.Clock()
        self.running = True
        self.load_data()

    def load_data(self):
        self.rocket_ship = pg.image.load(ROCKET_SHIP).convert_alpha()
        self.rocket_ship = pg.transform.scale(self.rocket_ship, (32, 32))

    def new(self):
        # Start a new game
        self.all_sprites = pg.sprite.Group()
        self.player = Player(self, WIDTH / 2, HEIGHT / 4)
        self.all_sprites.add(self.player)
        self.run()

    def run(self):
        # Game loop
        self.playing = True
        while self.playing:
            self.dt = self.clock.tick(FPS) / 1000.0
            self.events()
            self.update()
            self.draw()

    def update(self):
        # Game loop update
        self.all_sprites.update()

    def events(self):
        # Game loop events
        for event in pg.event.get():
            if event.type == pg.QUIT:
                if self.playing:
                    self.playing = False
                self.running = False

    def draw(self):
        # Game loop draw
        pg.display.set_caption("{:.2f}".format(self.clock.get_fps()))
        self.screen.fill(GREY)
        self.all_sprites.draw(self.screen)

        # After drawing everything, flip display
        pg.display.flip()

    def show_start_screen(self):
        pass

    def show_go_screen(self):
        pass

g = Game()
g.show_start_screen()
while g.running:
    g.new()
    g.show_go_screen()

pg.quit()

Answer 1

当你按UP时你不用改变速度，但是你要设置加速度：

~~self.vel = vec(PLAYER_SPEED, 0).rotate(-self.rot)~~

self.acc += vec(PLAYER_ACC, 0).rotate(-self.rot)

将加速度加到速度上：

self.vel += self.acc

我建议限制最大值。但是，我建议对每个方向分别执行此操作：

max_vel = 2
self.vel[0] = max(-max_vel, min(max_vel, self.vel[0]))
self.vel[1] = max(-max_vel, min(max_vel, self.vel[1]))

将此应用于方法 get_keys:

class Player(pg.sprite.Sprite):
    # [...]

    def get_keys(self):
        self.rot_speed = 0
        self.acc = vec(0, PLAYER_GRAV)
        keys = pg.key.get_pressed()
        if keys[pg.K_LEFT]:
            self.rot_speed = PLAYER_ROT_SPEED
        if keys[pg.K_RIGHT]:
            self.rot_speed = -PLAYER_ROT_SPEED
        if keys[pg.K_UP]:
            self.acc += vec(PLAYER_ACC, 0).rotate(-self.rot)
        if keys[pg.K_SPACE]:
            self.shoot()
        self.vel += self.acc + self.vel * PLAYER_FRICTION
        max_vel = 2
        self.vel[0] = max(-max_vel, min(max_vel, self.vel[0]))
        self.vel[1] = max(-max_vel, min(max_vel, self.vel[1]))
        self.pos += self.vel

你如何正确地对一个自由浮动的 space 物体施加重力，并在向相反方向推进时产生某种摩擦力

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